This invention concerns an electrically conductive floor covering based on linoleum which comprises a wear layer and an under layer, with the floor covering having an electrical contact resistance R1 in accordance with EN 1081 of a maximum of 107 xcexa9, and a method for producing the floor covering.
The market increasingly is demanding PVC-free, light-colored floor coverings with a low electrical resistance, in particular with a contact resistance R1 of a maximum of 107 xcexa9 (contact resistance per EN 1081 or electrical leakage resistance RA per DIN 51 953). Currently this demand is met only by electrically conductive rubber floor coverings. Such PVC-free, electrically conductive floor coverings based on rubber are described, for example, in DE 34 40 572 A1, DE 196 49 708 A1, and DE 35 45 760 A1.
Recently, however, there has been a heightened demand for floor coverings based on renewable raw materials, the classic example of which is linoleum floor coverings. A conventional linoleum floor covering has a relatively high electrical resistance of around  greater than 1010 xcexa9. Therefore such a linoleum floor covering cannot be used in rooms, the floor covering of which must have a certain electrical leakage resistance, such as, for example, in operating rooms of hospitals, laboratories, and computer rooms. Known for such applications is the reducing of contact resistance of the linoleum floor covering through the addition of electrically conductive fillers such as special carbon blacks. The addition of special carbon black, however, has the drawback that the use properties of the linoleum floor covering is deteriorated as a result of the relatively large quantity of carbon black required to achieve adequate electrical conductivity. Second, with the addition of carbon black to the linoleum mixture, possibilities for coloring are practically not present. Also in the use of metal powders for improving the electrical conductivity, the coloring possibilities are significantly restricted and in addition there are altered properties in the mechanical behavior as well as an increase in the weight and a significantly reduced thermal insulation of the floor covering. Therefore it has not been possible up to the present to achieve a conductive linoleum floor covering with bright color and contact resistance R1 of less than 108 xcexa9.
DE 3416 573 and WO 99/10592 concern electrically conductive floor coverings based on linoleum which through addition of at least one derivative of imidazol, imidazolin, benzixnidazol, or morpholin or a cation-active compound of the same is made electrically conductive or is antistatically equipped. Floor coverings of this kind, however, always have a contact resistance RI of approx.  less than 108 xcexa9, with this value additionally depending on the air humidity. In the case of dry air, even these values cannot be achieved.
WO 99/04085 describes a floor covering based on linoleum that is electrically conductive and on which the linoleum wear layer has an irregular pattern, for example marbling, of variously colored zones. The variously colored zones are delineated from each other with sharp contours and demonstrate varying electrical conductivity. Again the zones of this floor covering that are configured so as to be electrically conductive contain large quantities of a conductive filler material and are therefore very darkly colored. Although according to the document, a relatively large range of variation of color configuration appears to be possible, in accordance with example 4, by way of example, a third of the floor covering has a dark coloration. Furthermore, despite a relatively dark coloration, the contact resistances of the floor covering according to the document (6) are always only  greater than 107 xcexa9. It thus is also not possible with a method of this kind to produce sufficiently electrically conductive floor coverings that essentially have a light color tone throughout.
One objective of the present invention therefore is to provide a linoleum strip suitable as floor covering which has a low contact resistance R1, in particular a contact resistance R1 of a maximum of 107 xcexa9 which in addition is not as strongly independent [sic] on air humidity, and at the same time has a bright color ton. An additional task of the present invention is to indicate a method with which such a linoleum floor covering can be produced.
These objectives are solved with the objects characterized in the claims.
In particular a floor covering based on linoleum is provided that is electrically conductive and that has a wear layer (2) and an under layer (3), with the floor covering having an electrical contact resistance R1 of a maximum of 107 xcexa9 per EN 1081.
For determining the electrical resistance of floor coverings the following values are defined by EN 1081, which replaced DIN 51 953:
1. The contact resistance R1 per EN 1081, which corresponds to leakage resistance RA per DIN 51 953, is the electrical resistance of a floor covering measured on a sample between the tripod electrode on the surface of the floor covering and an electrode on the underside directly opposite it.
2. In contrast, according to EN 1081, resistance to ground R2, corresponding to resistance to ground RE per DIN 51 953, is the electrical resistance of a floor covering measured on an installed floor covering between a tripod electrode pressed onto the upper surface and ground.
Designated in the state of the art as xe2x80x9celectrically conductivexe2x80x9d floor coverings are floor coverings which have resistance to ground R2 measured according to EN 1081 of less than 109 xcexa9.
According to the invention, the floor covering has a contact resistance R1 of a maximum of 107 xcexa9 measured according to EN 1081. Also the resistance to ground R2 of the floor covering is preferably a maximum of 107 measured according to EN 1081.